Loans and Allowance for Loan Losses - Summary of Loan Portfolio by Risk Rating (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Credit Risk Profile by Internally Assigned Rating
Total Loans	$ 1,472,174	$ 1,356,778
Pass [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	1,443,592	1,320,970
Special Mention [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	13,961	23,970
Substandard [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	14,621	11,838
Doubtful [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	0	0
Residential 1-4 Family [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	357,360	350,758
Residential 1-4 Family [Member] | Pass [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	347,897	339,529
Residential 1-4 Family [Member] | Special Mention [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	5,500	7,681
Residential 1-4 Family [Member] | Substandard [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	3,963	3,548
Residential 1-4 Family [Member] | Doubtful [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	0	0
Multifamily [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	53,956	31,242
Multifamily [Member] | Pass [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	53,956	31,242
Multifamily [Member] | Special Mention [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	0	0
Multifamily [Member] | Substandard [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	0	0
Multifamily [Member] | Doubtful [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	0	0
Commercial Real Estate [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	603,283	564,965
Commercial Real Estate [Member] | Pass [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	586,317	545,301
Commercial Real Estate [Member] | Special Mention [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	7,721	13,313
Commercial Real Estate [Member] | Substandard [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	9,245	6,351
Commercial Real Estate [Member] | Doubtful [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	0	0
Construction [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	286,381	245,830
Construction [Member] | Pass [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	285,934	243,416
Construction [Member] | Special Mention [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	401	2,362
Construction [Member] | Substandard [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	46	52
Construction [Member] | Doubtful [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	0	0
Farmland [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	34,911	30,236
Farmland [Member] | Pass [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	33,888	29,260
Farmland [Member] | Special Mention [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	32	57
Farmland [Member] | Substandard [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	991	919
Farmland [Member] | Doubtful [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	0	0
Second Mortgages [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	8,053	9,026
Second Mortgages [Member] | Pass [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	7,488	8,007
Second Mortgages [Member] | Special Mention [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	290	347
Second Mortgages [Member] | Substandard [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	275	672
Second Mortgages [Member] | Doubtful [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	0	0
Equity Lines of Credit [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	47,958	41,496
Equity Lines of Credit [Member] | Pass [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	47,949	41,274
Equity Lines of Credit [Member] | Special Mention [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	0	176
Equity Lines of Credit [Member] | Substandard [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	9	46
Equity Lines of Credit [Member] | Doubtful [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	0	0
Commercial [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	27,278	30,000
Commercial [Member] | Pass [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	27,267	29,893
Commercial [Member] | Special Mention [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	11	18
Commercial [Member] | Substandard [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	0	89
Commercial [Member] | Doubtful [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	0	0
Agricultural [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	1,524	1,670
Agricultural [Member] | Pass [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	1,524	1,661
Agricultural [Member] | Special Mention [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	0	2
Agricultural [Member] | Substandard [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	0	7
Agricultural [Member] | Doubtful [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	0	0
Installment and Other [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	51,470	51,555
Installment and Other [Member] | Pass [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	51,372	51,387
Installment and Other [Member] | Special Mention [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	6	14
Installment and Other [Member] | Substandard [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	92	154
Installment and Other [Member] | Doubtful [Member]
Credit Risk Profile by Internally Assigned Rating
Total Loans	$ 0	$ 0